Automatic tuning control system



Aug. 6, 1940. w. E. NEWMAN AUTOMATIC TUNING CONTROL SYSTEM Filed July l0, 1937 3 Sheets-Sheet l Aug. 6, 1940. w. E. NEWMAN AUTOMATIC TUNING CONTROL SYSTEM Filed July l0, 1957 3 Sheets-Sheet 2 Gttorneg Aug. 6, 1940. w. E. NEWMAN AUTOMATIC TUNING CONTROL SYSTEM Filed July 10,'1937 3 Sheets-Sheet 3 nventor Patented Aug. 6, 1940 UNITE@ STATES ATENT OFFICE William E. Newman, Moorestown, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application Juiy 10, 1937, Serial No. 152,921

4 Claims.

The present invention relates to automatic tuning control systems for radio receiving apparatus and the like and more particularly to a system for automatic tuning of the electrical type wherein the tuning element of the controlled apparatus is actuated by electric motor means, as distinguished from present known systems employing mechanical means for the same purpose.

The present invention further relates to an electrical automatic tuning control system of the preselection type whereby any one of a plurality of preselected tuning adjustments may be effected automatically by the operation of a series of selector buttons or switches associated with or remotely located with respect to the apparatus controlled.

It is a primary object of the present invention to provide an improved and simplified automatic tuning control system of the electrical preselection type.

It is a further object of the present invention to provide a tuning-control system of the character above referred to which is provided with means for selective adjustment whereby it may function in response to manual, electric, or remote operation.

It is also a further object of the present invention to provide an automatic tuning control system of the type above referred to having a simplified electrical selector mechanism and a circuit in conjunction with a reversible electric 'motor means for operating the tuning control element of radio receiving apparatus and the like.

In modern radio receiving systems and the like, particularly of the superheterodyne type, automatic frequency control of the receiving circuits by present known means may be provided to elfect exact tuning of the apparatus to a received signal in conjunction with the normal variable tuning means, and it is a further object of the present invention to provide an improved automatic tuning control system embodying automatic frequency control and electrical preselection tuning control in combination whereby the electrical preselection control may effect approximate tuning for response to a predetermined signal, and the automatic frequency control may effect exact tuning subsequent to the operation of the preselection means.

Invan electrical type of tuning control an electric motor means is utilized for rotating the main tuning element of the controlled apparatus and, in accordance with the invention, operation (Cl. Z50-40) of the motor means, through movement of a portion thereof, is caused to engage mechanical means for actuating the tuning control element and electrical means for suppressing the automatic frequency control element until a prese- 5 lected tuning adjustment is effected by the operation of the motor.

It is, therefore, a still further object of the invention to provide an improved and simplified electric motor control system including a selection mechanism for a plurality of differing preselected tuning adjustments and means for automatically controlling the exact tuning operation in predetermined sequence.

It is also an object of the present invention to l5 provide conjointly operable electrical and mechanical control'means for selectively adjusting the apparatus for manual, electric and remote control in conjunction with an automatic frequency control system whereby the latter is suppressed or rendered inelfective by operation of the motor means. It is also contemplated that certain other portions of the receiving system may be controlled or rendered ineffective by the operation of the tuning control means, such as the sound output conjointly with the suppression of the automatic frequency control system.

The invention will be further understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings:

Figure 1 is a top plan view on a reduced scale of a portion of a radio receiver provided with an automatic tuning control system embodying the invention,

Figure 2 is a front view in elevation of the apparatus and system shown in Fig. 1 and is on the same scale as Fig. 1,

Figures 3 and 4 are cross-sectional views in elevation and plan, respectively, of a portion of the apparatus shown in Fig. 1, Fig. 4 being on an enlarged scale, and

Figure 5 is a schematic circuit diagram of an automatic tuning control system embodying the 45 invention and including the apparatus shown in Figs. 1 to 4, inclusive.

Referring to Figs. 1 to 4, inclusive, 5 is the chassis of a radio receiver on which is mounted a variable tuning control device 6 such as a variable condenser of the three-unit type, one unit of which is indicated by the dotted lines The tuning control device is of the rotary type. as is Well known, having a control shaft 6 which 55 is driven through a speed reducing mechanism from a tuning control shaft indicated at 9. 'Ihe speed reducing mechanism may comprise a pinion indicated at I on the inner end of the shaft 9 and a half gear II which meshes with the pinion I0, all as outlined in dot and dash lines in Fig. 2. As any suitable manual tuning control drive may be provided for the operation of the variable tuning condenser, further description is believed to be unnecessary.

Likewise, the tuning indication may be provided by any suitable means, such as by a pointer I2 movable over a series Vof scales indicated at I3 andY I4 across the face of the dial I5 through a connection provided by a cord I6 movable over a sheave II secured to the shaft 8, the cord being secured to the pointer which moves on a guide rail I8. Idler pulleys I9 are provided at each end of the scale for the cord I6.

The tuning control shaft 8 may also be driven electrically by an electric motor 2| through a gear train comprising arseries of gear Wheels and pinions 22, 23-24, 25--Z6, 2'I, 28 and 25, the last being mounted on the manual tuning control shaft 9 with the pinion IB and the remainder of the gears being mounted on xed pivots or shafts except the pinion 28,I which is movable into and out of meshvbetween the gear wheels 2l and 29 on a rocker arm 35 on a radius about the axis of the pinion I0.

When the rocker arm 38 and the pinion 28 are in the position shown the gear train is completed from the pinion 22 through to the main tuning control shaft 8 through the intermediary of the pinion I0 and the half gear Il, which is also used for manual tuning.

It will be seen that when the .rocker arm is moved counter-clockwise a short distance, the pinion 28 is withdrawn from engagement between the gears 21 and 29, thereby disconnecting the manual tuning `control elements from the motor of electric drive gear train. This permits easier manual tuning, since the friction load of the gear Atrain is removed from the manual tuning control shaft 9.`

The operation of the. link pinion 23 between the manual tuning control and motor drive gear trains is vactuated by a rotary `control shaft 33 mounted in the front apron of thechassis in a position to project .frontally therefrom on a line with other control shafts indicated at' 34, 35, 36 and 31 for various portions of the receiving apparatus.

A connection between the shaft 33 and the rocker arm 35 is provided by a lever 33 secured to the shaft 33 and rotatable therewith, and a connecting rod or link 39 pivotally connected with the lever 38, as indicated at '40, and also pivotally connected with the lower end of the rocker arm through a pin and slot connection 4l. The shaft 33 is rotatable to carry the arm 38 from `a positionshown in a clockwise direction to three angular spaced positions for operating a switch also connected with the shaft and mounted on the rear face of the chassis apron, as indicated at 42. The pin and slot connection 4I is such that the outer endofthe slot indicated at 43 engages the pin 4I and moves the low end of the rocker arm to the right when the switch is adjusted to its third position by clockwise rotation of the shaft 33. As shown, the shaft 33 and lever 38 -are in the eXtreme counter-clockwise position corresponding to a rst position "of adjustmentfor the switch 42. y'Connections forand operations of the switch will be hereinafter described.

The tuning motor is mounted on top of the variable condenser or variable tuning element for the purpose of facilitating assembly and adjustment. The motor is of the low voltage, alternating current, shaded-pole type and is reversible. The rotor, indicated at 45, is axially movable in response to energization of the motor in a frontal direction by action of the field thereon and is arranged for such axial movement when energized, for the reason that it is depended upon to 'eliminate operating relays and the like in actuating a switch and in closing a mechanical connection with the tuning drive gear train.

In the drawings (Fig. l) the motor armature is shown in its forward position and, for the purposeof permitting axial movement, the armature is mounted upon an extended motor shaft 46 journaled in spaced end bearings 41, the front end of the shaft being extended to a position adjacentto the initial pinion 22 of the `gear train and being axially in alignment with the pinion 22, as shown. The motor shaft engages the drive mechanism or gear train by a pin and arm coupling comprising a radial pin- 48 on the outer or front end of the motor shaft and a curved arm 49 secured to the pinion 22. This arrangement permits the motor to start without load as the shaft moves forward and rotation continues until the pinv and arm engage, thereby applying load to the motor after it has started. By this arrangement the size and power of the -motor may be reduced to a minimum, as is desirable.

The switch for controlling certain portions of the receiving system hereinafter describedmay be arranged to be actuated by the axial or longitudinal movement of the motor shaft when energized and in its present preferred form comprises a plurality of spaced elongated flat spring elements 50, 5I and 52 secured adjacent one, end to a frame 53, on which the motor is mounted, between insulating blocks indicated at 54. `r

The opposite ends of the flat spring switch members extend radially. inwardly toward. the motor shaft to a position wherein lthe `spring member 5I) more adjacent to the armature may be engaged and moved by a collar1 55 securedA to the shaft when the latter moves forward in. response to energization of the motor. The spring vmember 50 extends aroundthe shaft in spaced relation thereto and .is also provided with a washer 56 between the collar and .the spring member.

vThe operation of the motor shaft in connection with the switch is such that pairs of con.- tacts 6B and 6I are closed to connect the switch springs as the motor shaft moves forward. to cause the driving connection between the motor shaft and gear train or drive mechanismto be established. 4These contacts, as will hereinafter be described, vcause the receiver .output to be silenced or reduced and the automatic frequency control system to be suppressed, whereby the latter may come into operation to effect exact `tuning to a predetermined station or signal subsequent to the main tuning operation ,by the electrical means. In addition, theaxial movement of the motor shaft, in combination with the pin and arm drive, provides quick disengagement of the motor from the mechanism driving the tuning element or condenser when the'motor is deenergized.

The motor is energized, through a plurality of individual selector switches 65-66 (Fig. 1) associated with the tuning dial and arranged, in the present example, in two rows, of four each at opposite sides of the dial. The switches are actuated by individual buttons indicated at 61 and E8 carried by the escutcheon o1' panel front indicated at 69.

'I'he motor energizing circuits through the individual switches are connected in parallel and each circuit includes a connection to ground or chassis through a spring contact and a selector ring 'il (Fig. 3) in a selector mechanism 'I2 positioned at the rear of the tuning element of the receiver and connected for rotation therewith. The number of rings in the selector mechanisin correspond to the number of selector switches and buttons and may be provided in any desired number within reasonable limits to permit preselection of a desired number of stations or signals. In the present example, eight selector switches and eight selector rings are provided, although the system is not limited to this number. However, it has been found that there are usually not more than eight stations normally available in any locality lfor constant daily reception and therefore this number of selector switches and rings is shown by way of example as a practical embodiment of the invention.

The motor circuit is closed to energize the motor by operation oi the switches indicated at Sil and t6 and is opened to deenergize the motor by one of the individual elements of the selector mechanism, such as that shown more clearly in Fig. 3, the circuit being opened when the spring contact lit disengages from the metallic ring 1l and sweeps upon a narrow insulating segment 'liainserted in the periphery of the ring at a point diametrically opposite to a slot 13. The arrangement, therefore, is such that the selector switches serve to energize the motor and the selector mechanism serves to deenergize the motor, causing it to stop when the circuit is opened at a predetermined point corresponding to the position of the insulating segment on each ring with respect to the tuning mechanism, as will hereinafter be described.

The switches on the panel comprise elongated spring contact fingers 15, 1B secured at one end and having free ends which are brought into engagement as indicated at 'l1 when a button such as the button 61 is depressed.

Each button bears against agrounded metallic strip it, one :tor each switch, which serves to move the outer contacts i6 against the inner contacts l5 and to hold the contacts in engagement. A strip of insulating material is provided be tween. the operating iinger or strips 'iii and the outer contacts le, indicated at 19. The flexible or free ends of the operating strips for the buttons provided with a detent, as indicated and a cam shaped surface indicated at moving and engaging with a pivotedatch me ber indicated at 82. The latch members are a.; auged to engage with any one of four operating strips cn each side oi the dial and interconnected by a link member 83 so that movement of one M serves to move the other and to ren tl... switch contacts previously engaged. In Fig. l the uppermost switch member is shown closed with the latch engaged with the operating member is. Both latch members operate about pivot axes indicated at 8d under the action of retracting springs 85. The switch members and the operating iingers are of spring materiai tending to assume the position shown at the left side of Fig. 1 when released. from the-closed position shown on the right side of Fig. l, the switches being thus normally in the open circuit position.

The selector mechanism is mounted as a unit assembly at the rear end of the variable tuningr capacitor, as shown more clearly in Figs. l, 3 and e and comprises the unitary frame 8S in which is journaled a shait Si. in alignment with the condenser shaft i? and connected therewith by a iiexible mechanical coupling means B.

The rear end of the shaft 8i carries a movable arm 30 which vactuates a reversing switch dfi having an operating lever E! which lies in the p." th of movement of the arm, whereby' the switch actuated at the extreme ends of the travel of the tuning mechanism to cause the motor to reverse the direction of operation of the tuning shaft. This arrangement greatly simplies the switching arra logement for stopping the motor at predetermined positions and permits the use of single brush contacts and grounded contact rings in the selector mechanism as well as a ies con-- trol circuit for the motor, as will herei e api' when considering the circuit diagram.

The selector mechanism comprises a series oi stacked washers spring discs secured to the selector shaft lil, as shown more clear' in Fig. 2l. The selector rings ll are preferably oi ,ir-ass and are unted to rotate on relatively7 large diameter di ,s or washers fit between pairs oi spring discs which frictionally engage and grip the contact rings between their peripheral edges. S' diameter spacing washers iil of steel ,it Si for easy adjustment. Each ring is proeo. with a slot 'i3 and with a diametrically :row insulating segment or gap 12o .,xible spring contact 'lil is associated with as indicated in Figs. i and The u' cont lil mounted on a suitable strip oi insulating materiai. @S carried by the frame Sii. The spring contacts bear against the contact rings at the peripherles thereof and when the insulating segment or gap of a contact ring reaches a ycontact finger, the motor circuit is caused to be opened and the stopping position or" the tuning mechanism is thereby determined when driven by the electric motor The selector rotor may be considered as consisting of a plurality oi independently adjustable spring disc and ring assemblies made up by stack.- ing a plurality of circular elements on the shaft comprising spring washers and spacers. Each ci the adjustable rings may be locked in a iixed position inserting a lie f member 94 through aligned guide openings or holes 55 and Sii, respectively, a bracket til' and the frame 86 at the top of the frame, and seating the end key member in the slot 'i3 in the contact ring directly below, as shown more clearly in Fig. 3. Thus, by inserting the key in any one ci the holes so that registers with the key slot on its respective contact ring, it is possible to lock the ring in position sc that it will not turn when the con denser rotor is rotated. This enables the setting or logging oi stations anywhere within the rotatable range of the condenser. rlhe stations i..- he logged close together with this arrangement since the Contact rings are independently adjustable, one with respect to the other, and when one is adjusted the others are not disturbed.

When the key SF. is not in use it is inserted in an opening 58 in a flexible rubber bushing S9 llil.

located in the top of the frame 86.

The selector mechanism frame is mounted at the rear of the condenser frame by suitable studs l@ ia without imparting a mechanical strain upon the condenser frame. As indicated by Fig. '3, a stud ltlB is interposed between the selector mechanism to supportA the selector mechanism during shipment, this stud being disengaged when the receiver is put into operation.

The electrical circuit arrangement employedin connection with the mechanism shown in Figs. l to 4, inclusive, is shown in Fig. 5, to which attention-is now directed and in which the circuit elements and parts which have-been referred to. in the preceding gures are designated by the same reference numerals.

Referring to Fig. 5, the manual tuning control shaft 9 is shown connected with the variable tuning control shaft 8 of the variable tuning control included within the rectangle H0 which, in the present example, may include the variable tuning capacitor or condenser unit hereinbefore referred to and is connected with the selector mechanism shaft 81 which carries the selector rings l'i between the spring discs lllll for rotational adjustment with respect to the shaft 871. The outer end of the shaft carries the arm't' for operating the reversing switch 90 by means of the operating lever 9|.

The contact rings may be held against rotation by the key 94 which causes the insulating segment '52a to align exactly with the contact members or brushes l!) for the various contact rings. Tuning is then manually adjusted for a prede termined desired station by means of a suitable tuning indicator such as a tuning indicator tube This tube is located directly over the dial` as shown in Fig. 2. When the station is exactly tuned in by means of the tuning indicator tube, the key 94 is removed and the same operation is repeated for the various other selector rings until the required number of preselected stations or positions of adjustment of the tuning mechanism are obtained up to and including eight, in the present example. In Fig. 5, only three of the rings are shown for the purpose of simplifying the drawings.

The rotor 5 of the electric motor is shown in connection with the pin and arm connection with the gear train or driving mechanism for the variable tuning control means and also in connection with the switch comprising the contacts 5l), 5i and 52. The link pinion 28 schematically indicated in connection with the gear train and in connection with the selector switch ft2, by the dotted connection H2. The motor circuit is arranged for reversing by means of `the reversing switch 9|] at the end of the travel of the tuning mechanism and for this purpose the motor is provided with supply terminals H3, H4, 'between which are connected operating windings H5, and is further provided with a reversing winding H6. The latter is connected between the operating windings H5 and through the reversing switch and may be connected with either of the terminals H3 or H. For this purpose, the reversing switch is provided with a reversing contact connected with the winding H6 and to reversing contacts H3 connected with the terminals H3 and Hli 'selector mechanism vthrough leads indicated at H9.

Power is supplied to the motor from a low voltage secondary winding on the power transformer |2| of the receiver, one side of the secondarybein'g grounded 'asindicated at |22. The remaining side of thesecondary |20 is connected through `a lead `|23'with oneA of the motor terminals' H4; The other motor terminal is connected .to'ground through any one of a plurality of selectable parallel series circuits, each containing one of the contact rings 7| and corresponding contact brush it, and one of the selector switches comprising elements 'l5 and 16.

`The Vvconnection to ground places the motor across'the secondary |20 and causes it to operate in a direction determined by the position of the reversing switchV 953. The parallel grounding circuits are those provided for the various selected rings and in the present example may be eight in number, although, for the sake of simplifying the drawings, only three yarev shown in the circuit diagram of Fig. 5. The electric selector buttons or switches are inclu-ded in the dotted rectangle |25, which are the switches adjacent to the tuning dial, and the Contact members are provided with the same reference numerals.

, It will benoted that the contact arms .it are connected toy a common lead |26, while the fixed contacts l5 are each connected to a separate lead such as the leads |27, |28 andV |25 leading to a separate one ofV the selector contact brushes lil. With the brushes in contact with the selector rings, the circuit is completed to ground through having a series of'button operated switches for effecting thesame .connections asin the unit 25 at the receiver. This contains the same number of switches or selector contacts as the selector switches at the receiver and in the present example only'three areshown- The switches comprise movable contacts i3? and xed contacts |38 operating selectivelylto control the same circuits as the switches in the unit |25. For this purpose, the XedcontactslS are connected through extensible leads indicated at |39 with the xed contacts 15 in the local control unit at Athe receive-r.

The movable contacts i3? are connected in parallel to an extensible lead l corresponding to the lead |26 for the unit |25.

The selector switch 132.' is provided with a rotary control element or insulating member |40 which carries a pair of contacts |4| bridging twol adjacent fixed contacts, such as the contacts |32 and 311 and is movable from the position shown in a clockwise direction, as indicated by the arrow.

In the position shown, the motor circuit is connected to the remote control unit |36, the connection extending from the terminal i3 through the lead |33, across the contacts |32 and |34 through the jumper connection |1i| to the lead |35 and thence the contacts lfi` and |38 in the upper switch of the remote control unit to one of the leads |39 correspondingto one ofthe selector mechanism contact rings. ample, the rst or left-hand ring is shown in the open circuit position to interrupt the motor circuit at the contact 10 thereby stopping the tuning mechanism. In either position on opposite sides of the insulating segment 12a, the contact IB closes with the periphery of the selector ring and the circuit is completed through the shaft 8l to In the present exground |30 and thence A.to the secondary |20 through the ground |22.

With the selector ring held in position by the key 94, the manual tuning of the receiver to a desired station is effected and thereafter, with the key Sl removed, the tuning mechanism will come to rest in the same position by the opening of the motor circuit at the contact irl when it engages the insulating segment 12a. Any oi the other keys may be depressed to'close the switches corresponding to the selector rings, either in the remote control unit or the local unit |25, and for the latter the switch i2 is movedclockwise to a second position to cause the contacts 3l and |32 to be connected by the bridging or jumper contact IM, thus completing the motor circuit through the lea-d |25 and any one of the selector switches in the unit 25, as hereinbeiore described for the remote control unit.

In a third position of clockwise movement from the switch i2, the bridging. contact ifll is connected between the contact itl and a blank contact |42, thereby opening the motor circuit and preventing operation by the electric or the remote control means. At the same time the mechanical connection indicated at H2 and hereinbefore described, particularly in connection with Fig. 2, causes the link pinion it to disengage from the gear train, permitting free tuning movement for manual operation by means of the shaft il without driving the load caused by the gear train.

The positions of the selector switch 42 may be suitably indicated by electric lamps indicated at |44 and |45 through the medium of suitable fixed switching contacts Hifi, i137! and M3. For the control of said contacts, a second bridging conductor mounted on the movable insulating element itil is provided at ifi@ and in the position shown bridges between the fixed contact |48 and a blank contact itt. Energy for lighting the lamps |44 and M5 is provided by the low voltage secondary of the power transformer |21 which is utilized to energize the heaters and iilaments of the receiving system. This secondary is indicated at |5| and is also grounded, as indicated at 52, at one terminal. The opposite terminal is connected through a lead |553 to both or" the lamps in parallel and from the opposite side of each lamp a separate lead is taken to the switch lit. A lead |54 for the lamp lili connected with the terminal Mill, while a lead ist@ for the lamp |45 is connected to a termina-l llfi. The terminal |41 between the terminalsv 'i it and M31 is connected to ground as indicated at l.

Since the switch is shown in the remote control position, the lamp circuit is opened and no indication is provided. When the switch is moved to electric control for local operation of the electric tuning at the receiver, the contacts' lili?. and |41 are closed by the bridging contact lili), thereby closing the supply circuit through the lamp |44 from the lead |53 to ground |56 and to the secondary When the switch is moved to the third position for manual tuning the circuit is closed to the lamp M5 and the |54 in a similar manner indicating manual tuning. The lamps may be placed behindsuitable indicating windows .in the receiver panel front as indicated in dash lines in 2 at |51 and iii, the lamp IM being placed behind the translucent window |51 and the lamp M5 being placed behind the translucent window |53. The windows may include suitable legends as indicated.

The `automatic frequency control system includes a tuning control tube indicated at it@ and is responsive to signals applied to a control grid 6| through a grid leak |62 in connection with a grid capacitor |63 from a control lead |64. Since the control lead is connected with a source of lbiasing potential which varies in polarity and magnitude with variations in frequency on either side of resonance, in the present example, this potential is derived from the automatic frequency control rectifier tube indicated at |55 across an output resistor comprising two sections |66 and |61, the latter being connected to ground as indicated a-t |65. The lead |64 is connected to the ungrounded terminal |69 of the output resistor Automatic volume control potentials are derived from the resistor |61 through a lead |13 and controlling potentials are also applied to the tuning indicator tube through alead 1| connected through a suitable lter comprising a resistor |12 and by-pass capacitor |13. As is well known, the tuning indicator tube illustrated is of the RCA 6F15 type, in which a dark segment oi varying width appears upon a colored background or screen. The tuning control tube operates to vary the frequency of a portion of the receiving circuit to cause a desired intermediate frequency to be produced whenever a signal is approximately tuned in by the electric tuning mechanism, thereby causing the tuning of the receiver system to exact resonance with the received signal.

Both the selector switch 42 and the contacts associated with the electric tuning motor are arranged to suppress the automatic frequency control operation. For this purpose, the lead |64 is connected with fixed contacts |15 and E16 in the switch 42. A blank contact |11 is provided adjacent to the contact |1t` and a grounded contact |13 is provided adjacent to the contact |15. A series of contacts are arranged to be bridged by a bridging connection |19 carried by the c rotor |49 of the switch. In the remote control position shown, the contacts |11 and |15 are connected and the automatic frequency control system is operative. Likewise, it is operative in the electric control position when the contacts |15 l and llt are bridged. However, in the manual position, which is the third position in a clockwise direction. the contacts |15 and |18 are connected to ground the lead |54, thereby suppressing automatic frequency control of the tunf ing system.

This suppressing connection for the automatic frequency control system is likewise provided by the contact 5i! in the switch associated with the tuning control motor which is connected through a lead |83 with the lead ltd. It will lbe noted that the contact 52 is grounded and when the motor armature moves upon energization of the motor, the contact ll is connected through the contact 5| to the contact 52 and ground, thereby suppressing automatic frequency control of the tuning system and preventing the automatic frequency response to adjacent channel signals in passing', where the adjacent channel signal is relatively strong with respect to the selected sig- 13" nal, for which the tuning system is adjusted to stop. When the motor is deenergized, the automatic frequency control suppression is removed by opening of the contacts 5|), 5| and 52 and the automatic frequency control system completes In ordervthat the receivingsystem' may not emit' sounds when tuning by electric or remote control means, a portion of the receiving system may be arranged to cut off the signals transmitted therethrough and this is most readily obtained by short circuiting a portion of the audio frequency amplifier to ground.

In the present example, the grid circuit |8| of an audio frequency amplifier tube |82 is short circuited to ground through a lead |83 connected with the switch'contact 5|. The tube |82 is in the audio frequency amplifying channel, as indicated, and it will be seen= that when the contact 5| closes with the contact 52 the audio frequency channel will be short circuited, thereby suppressing signals passing through it.

From the foregoing description, it will be seen that in a tuning system in accordance with the invention a reversing switch is arranged to 'change the direction of rotation of the tuning motor at the end of the travel of the tuning control element in either direction and operates in such a manner that in case the selected tuning position is on the side of the setting already passed over by the selector mechanism, the station is then approached, i. e., the tuning position is approached from the opposite direction. This simplies the tuning mechanism and circuit as has hereinbefore been referred to and the additional time for travel is compensated by providing a high speed motor'.

The selector buttonsr are interlocking `whereby a depressed Ibutton is released upon the selection of a second button so that the operation of the system is not interfered with under the co-ndition that two buttons should be depressed at the same time. If this is done, however, it will be seen that the selector mechanism will hunt between the two selected positions and become continuously movable from one end of the scale to the other without stopping. The tuning indicator tubeis utilized for manual tuning and for initially setting the frictionally held contact rings for station selection. Automatic frequency control is not operative for manual` tuning and is controlled by the manual-electric-remote selector switch, as well as by the end movement of thc motor armature.

By `providing locking switch contacts, a selected station may be tuned in without waiting for the motor to operate while maintaining pressure on the button. Likewise, the operation of setting up a plurality of selected stations or stopping positions for the tuned mechanism is facilitated by the location of the selector mechanism at the rear of the tuning element and providing a plurality of relatively widely spaced contact rings in a single circuit connection wherein a minimum number of contacts are provided and wherein there is no problem of controllingpressures or contact adjustments. .Thesimple commutator arrangement and reversing switch directly on the condenser shaft causes the operation to be positive and eliminates frequent servicing. The motor circuit is closed by a simple two-point switch and is opened by a simple insulated gap or segment in a plain metallic ring rotated in frictional engagement with the condenser shaft. The system is adapted as well for electric preselection tuning as for remote control and the circuits and switching control elements may be a supplication of the circuits and control elements on the-receiver, thereby simplifying construction and installation, as well as operation.

I claim as my invention:

1. In a radio receiving system including variable tuning means provided with a control shaft and a motor for driving said shaft, the combination of means providing a gear train between said motor shaft and said tuning control shaft, a selector mechanism comprising a plurality of con' tact rings frictionally coupled to said tuning control shaft and each provided with an insulation segment at its outer periphery and with -a contact member engaging said periphery, local and remote groups of interlocking control switches connected in the circuits of said contacts for selectively energizing said motor through said rings, and selector switch means for rendering only one of said groups effective to control said energication, and for rendering both of said groups ineffective, and means for conjointly operating said selector switch means to render both of said groups ineffective and for removing the load of said gear train from the tuning control shaft.

2. In a radio receiving system, the combination with variable tuning means having a control shaft, automatic frequency control means and resonance indicating means, of electric motor means having a shaft which moves axially in response to energization of the motor, switch means responsive to axial movement of said shaft for electrically suppressing the automatic frequency control means and the signal output from said receiving system, means providing a gear train between said motor shaft and said tuning control shaft, means for mechanically disconnecting the gear train from said tuning control shaft whereby said last named shaft may be manually operated without the load of the gear train thereon and conjointly suppressing the automatic frequency control means, a selector mechanism connected with said tuning control shaft to rotate therewith and including a plurality of axially spaced contact rings, each of said rings havin-g a narrow insulating gap in the periphery thereof and a contact member engaging said periphery, interlocking control switches, one in circuit with each contact member for selectively energizing the motorv means therethrough and means for adjusting the angular relation of the tuning control shaft to said insulating gaps by said manual tuning control means in conjunction with said resonance indicator means.

3. In a radio receiving system, the combination with a variable tuning means provided with a control shaft, of a reversible electric motor for driving said shaft, a speed reducing gearing providing a driving connection between said'motor and said control shaft, said gearing and said motor being .providedl with coaxial shafts and radially extending members adapted to provide a connection between the motor and the gearing, said motor shaft Ibeing axially movable to effect said connection, a reversing switch for said motor provided with means whereby it is controlled by the end movement ofthe rotation of said control shaft, means Vproviding a plurality of contact rings frictionally coupled and grounded to said control shaft and each being provided with an insulation segment at the periphery thereof and with a Contact member engaging said periphery, a plurality of control switches each connected in the circuit of a different one of said contacts and with said motor for selectively energizing said motor through single circuits including a common ground, automatic frequency 'control means for said system having a control circuit', a selector switch insaid control circuit and connected with said motor 'circuit for rendering said control switches and said automatic frequency control means ineffective, and means connected with said switch and conjontly operable therewith for removing the load of said gear train from said control shaft When said selector switch is operated.

4. In an automatic tuning device for radio receivers, a tuning shaft, an electric motor, means for transmitting motion from the -motor to said l0 tuning shaft, means for stopping said motor at one of a plurality of predetermined Ipositions of said tuning shaft, an automatic frequency control circuit, a switch in said circuit movable to a :position in which the circuit is rendered inoperative, and means for preventing transmission of motion from said motor to said tuning shaft in response to movement of said switch to said position.

WILLIAM E. NEWMAN. 

